Process for the preparation of ethylene polymers



Oct. 30, 1945- c. H. GREENEWALT 2,338,138

PROCESS FOR THE PREPARATION OF ETHYLENE POLYMERS Filed Jan. 29, 1943 Caged QMSGEQ QQQQQQEQ [raw/a'm'li @fQQJZQWtZ/f INVENTOR.

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6 Claims. (Cl. 260-494) This invention relates to an improved process for the polymerization of hydrocarbons contain ing a single ethylenic linkage and is more particularly related to an improved process for the polymerization of ethylene to products of relatively high molecular weight. 7

Various methods have been proposed for the polymerization of oleilnes such as ethylene with the principal object of obtaining high molecular weight products for various purposes. Oil-like products of relatively low molecular weight have been prepared from ethylene by its polymerization in the presence of boron fluoride and like catalysts while solid to semi-solid high molecular weight productsof a polymeric nature have been obtained by effecting the polymerization in the absence of catalysts or in the presence of peroxygen-type catalysts by treatment at pressures above 50 atmospheres and up to 3,000 atmospheres or more. The invention of the instant case is principally directed toward products of the latter type.

An object of the present invention is to provide an improved process for the polymerization of hydrocarbons containing an ethylenic linkage,

Another object is to provide a process for the preparation of high molecular weight products from ethylene wherein the ethylene is brought to reaction pressure in two pressure steps. A further object is to provide an improved process for the preparation of polymers of ethylene wherein the ethylene is compressed, liquefied at relatively low pressures and the liquid ethylene subsequently raised to polymerization pressures. Other objects and advantages of the invention will hereinaiter appear.

In the preparation of high molecular weight polymers of oleiinic hydrocarbons containing an ethylenic linkage and more especially in the polymerization of ethylene per se and the preparation of high molecular weight polymers of ethylene with other organic compounds, in the presence of peroxygen-type catalysts or if very high pressures are used in the absence oi! added catalysts, the reaction is conducted under superatmospheric pressures. In accord with the invention it has been found that the ethylene or other oleflnic hydrocarbons can be eillciently and economically brought to reaction pressure by first compressing the gas to approximately its critical pressure, and for ethylene preferably to a pressure between 20 and 150 atmospheres, subse- .quently cooling the thus compressed gases to a. temperature suillcient to liquefy them, that is, for ethylene, to a temperature between -35 and 0., thereby converting the gas to a liquid, and thereafter raising the pressure of the resulting liquid to the desired reaction pressure.

By carrying out the compression in accord with the above general procedure and by the use of available compression means, valuable products are obtained uncontaminated with forei n substances which may be introduced into the oleilnes unless the indicated procedure is followed. It has been found that ethylene under pressure is a solvent for mineral and vegetable hibricating oils and consequently when the vapors of ethylene and like oleflnes are compressed they pick up the lubricants employed in the compressors and carry these lubricants into the product. This contamination should be avoided inasmuch as high molecular weight products and polymers of ethylene containing these lubricants are not as valuable or as useful as similar products obtained in pure form.

By the pressure cycle of the present invention, it is possible to carry on the first step of compression in a compressor lubricated with minem] or vegetable oil inasmuch as at the comparatively low pressures of this step, i. e. up to about 150 atmospheres, the oleflne will not pick up undesirable quantities of the lubricant. After refrigeration to a liquid, the liquefied oleflnes may then be raised to the high reaction pressure in a liquid injection pump (wherein contact with the lubricant is slight), or in any other suitable pump in which contact of the oleflne with the lubricant islimited.

The invention will be more easily understood by reference to the attached diagrammatic drawing, wherein ethylene from gas holder I is drawn through an oil lubricated compressor 2 and its pressure increased to from 20 to atmospheres. Inasmuch as ethylene will contain some moisture, it is passed through a drier 3, containing calcium chloride, solid NaOH or other suitable drying medium, for the removal of the moisture and is then passed into a refrigerating chamber 4 wherein it is condensed to a liquid. Prior to or subsequent to its passage into the refrigerating chamber 4, benzene or other suitable addition agent such as lsooctane, chlorobenzene, etc., or a reactant such as vinyl acetate, vinyl chloracetate, methyl methacrylate, etc., may be introduced, by means of the injector la from storage tank 5 into the ethylene. Benzene may be introduced at a rate of approximately 0.05 to 2.0 parts thereof per part of the ethylene, other addition agents being introduced in suitably controlled amounts. The resulting liquid mixture is then raised in the injector I to the pressure of polymerization preferably between 800 to 1500 atmospheres although much'higher pressures may be used, The resulting mixture is then heated to the desired reaction temperature, in preheater I, i. e. for example, between approximately 50 and 400 C. after which the compressed reaction mixture is introduced directly into the converter '0. Into converter 9 there is likewise injected 0.1 to 10.0 parts of water per part of the ethylene, the water being transferred from the storage tank I to the oxygen saturator I0, is heated in preheater II and forced into the converter 9 by means of the injection pump it. The total oxygen at this point should be equivalent preferably to about 20 to about 2000 P. P. M. of the ethylene present. The products issuing from the converter pass through a pressure let-down valve I! from which they are introduced into the product receiver II. The solid products are discharged from the bottom of ethers, divinyl formal, divinyl vinyl kctone. This olefinc a,sas,1ss i V inierpolymers with vinyl rum chloride, vinyl cyanide and N-vinyl amides, vinyl will likewise form high molecular weight products in the presence of and with a number of compounds such, for example, as the halogenated aliphatic hydrocarbons; saturated aliphatic or aromatic acids, esters, an-

hydrides, aldehydcs, alcohols, ethers and so forth; and with sulfonyl halides, and sulfur halides.

I claim:

1. In a process-for the polymerization of ethylene in the presence of a catalyst selected from the product receiver M. The vapors from the top or receiver I are returned to the ethylene stream after cooling in cooler 20 to approximately inlet ethylene temperature, condensed water and benzene being separated from the oleflne in cooler 20. The cooled ethylene is then returned to the synthesis with the make-up ethylene stream.

The reaction as broadly described above may be carried out in accord with the invention in any suitable type of converter capable of withstanding the high pressures and it is preferably conducted in one having relatively great length to cross section. The converter may be made of high chromium, low nickel steel such as 18% chromium 8% nickel or may be made of alloy steel or mild steel lined with a chrome-steel or other suitable metal such as silver, or with other corrosion resisting liners of chromium, porcelain, etc.

The peroxygen-type catalyst which may be employed with the reaction includes molecular oxygen or air which may be present with respect to the oleflne' in amounts ranging from 5 to 2,000 P. P. M. (calculated as oxygen). While oxygen is the preferred catalyst other peroxygen-type catalysts may be used, such catalysts including dialkyl dioxides (such as diethyl peroxide), hydrogen peroxide, persuccinic acid, lauroyl peroxide, tetralin peroxide, urea peroxide, butyryl peroxide, benzoyl peroxide, alkali metal and alkaline earth metal and ammonium persulfates, perborates, percarbonates and the like. The amount of peroxide catalysts used may vary over a wide range from 0.1 to 5% by weight based on the ethylene or higher. I

The reaction-as has been stated may be conducted withany polymerizable aliphatic monooleflnic hydrocarbon by which is meant one that can be converted to a polymer in the presence of the aforesaid and like catalysts under the pressure and temperature conditions designated. Ethylene, propylene and isobutylene are the most prominent hydrocarbons of this class and of these the most important is ethylene.

The invention is not limited solely to the polymerization of the aforesaid hydrocarbons for it is known that ethylene can be inter-polymerized with a variety of unsaturated compounds such as propylene, isobutylene, styrene, and similar monooleflnic hydrocarbons, vinyl esters, such as vinyl acetate, vinyl formate, and vinyl isobutyrates, as well as such acids as acrylic, methacrylic, itaconic, crotonic, and fumaric as well as their derivatives such as esters, acid halides, amides, and

anhydrides. Ethylene will likewise form valuable the group consisting of oxygen and peroxy catalysts at pressures between 800 and 3000 atmospheres,-the operation which comprises compressing the ethylene to between 20 and atmospheres, refrigerating the ethylene under this pressure to a temperature between 35' and 5 (2., thereby condensing it to the liquid phase, and subsequently increasing the pressure, in the substantial absence of lubricating oil, of the liquid ethylene to polymerization pressures between 800 and 3000 atmospheres.

2. In a process for the preparation of solid to semi-solid polymers of ethylene in the presence of an organic peroxide catalyst at a pressure between 50 and 3000 atmospheres the operation which comprises compressing ethylene to between 20 and 150 atmospheres, refrigerating the ethylene under this pressure to condense it to a liquid phase, and subsequently increasing the pressure, in the substantial absence of lubricating oil, of the resulting liquid to polymerization 3. In a process for the preparation of solid to semi-solid polymers of ethylene in the pncsence of an organic peroxide catalyst at a pressure between 50 and 3000 atmospheres, the operation which comprises compressing ethylene to between 20 and 150 atmospheres, refrigerating the ethylene under this pressure to a temperature between 25 C. and +5 0., and subsequently increasing the pressure, in the substantial absence of lubricating oil, of the resulting liquid to polymerization pressure between 800 and 3000 atmospheres.

4. In a process for the preparation of solid polymers .of ethylene in the presence of an organic peroxide catalyst and under pressures between 50 and 3000 atmospheres, the operation which comprises compressing ethylene to between 20 and 150 atmospheres, refrigerating the ethylene under this pressure to a temperature between 25 C. and +5 C., compressing benzene to substantially the liquefied ethylene pressure, adding it to the liquefied ethylene and subsequently increasing the pressure, in the substantial absence of lubricating oil, of the benzene and liquid ethylene mixture to polymerization pressure between 50 and 3000 atmospheres.

5. In a process for the preparation of solid to semi-solid polymers of ethylene in the presence of an organic peroxide catalyst at pressures between 50 and 3000 atmospheres, the operation which comprises compressing ethylene to between 20 and 150 atmospheres, compressing benzene to substantially the same pressure, mixing the combutyralandmethyl semi-solid polymers of ethylene in the presence of an organic peroxide catalyst at pressures between 50 and 3000 atmospheres, the operation which comprises compressing ethylene to between 20 and 150 atmospheres, refrigerating the ethylene under this pressure to a temperature between -25 C. and +5 C., introducing benzene into the liquid ethylene, increasing the pressure, in the substantial absence of lubricating oil, of the benzene and liquid ethylene mixtures to polymeriza- 1 tion pressure between 50 and 3000 atmospheres, admixing the organic peroxide catalyst with the compressed mixture, effecting the polymerization at temperatures between 50 and 400 C., dropping the pressure on the reaction mixture, separating the polymers of ethylene from the unreacted ethylene and the benzene, and thereafter separating the benzene from the ethylene and returning the ethylene to the reaction.

CRAWFORD H. GREENEWALT. 

